CORN
Crop Observation and Recommendation Network

May 13 - 20, 2002
C.O.R.N. 2002-13b

In This Issue:

A) Wheat Development, Wet Weather And Wheat Diseases
B) Barley Yellow Dwarf In Wheat
C) Corn Seed Treatments: What To Expect
D) Watch For Slugs And Bean Leaf Beetles
E) Field Guide Revised
F) Insect Pest Bulletin Revised
G) Alfalfa Weevil Update
H) Wet Weather Brings Wild And Wooly Burndown Situations
I) Adjusting Herbicide Programs For Late Planting
J) Early Postemergence Application Of Residual Corn Herbicides
K) Growing Degree Days Available For Late Corn Plantings
L) Management Considerations For Late Planted Soybeans

Click here to view the first half of this weeks newsletter (2002-13a)

A) Wheat Development, Wet Weather And Wheat DISEASES - Pat Lipps CORN Questions

Wheat in southern Ohio (Ross Co and south) is in head (Feekes growth stage 10.3) and many fields in flower (growth stage 10.5.1). In central Ohio up to St. Rt. 30 the wheat is in boot stage (growth stage 10). In northwest Ohio the wheat is in flag leaf emergence from growth stage 8 to 10. Weather conditions during the period of head emergence through flowering is extremely important to the occurrence and development of Fusarium head scab. This disease has caused significant yield losses in Ohio as recently as 1996 when the state yield average was only 39 bu/A due to scab when the average should have been in the mid 60 bu/A range. Over the past few years head scab has not been too much of a problem in Ohio because the temperatures during the heading and flowering periods have been relatively cool, limiting fungal development and infection of the wheat head. We are currently monitoring the weather conditions at various locations in the state and the crop development to determine the risk of head scab. We will be placing our scab risk predictions for various locations in the state on the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease and reporting the predictions in each CORN newsletter over the next several weeks.

We are currently working with two scab risk prediction models. One model uses weather conditions seven days prior to flowering of the crop to make a preliminary prediction for scab risk. The other model uses the weather data from seven days prior to flowering and ten days after flowering to make a prediction of scab risk. This second model is more accurate in predicting the scab risk because more weather data is available on which to base a prediction. Our first reports will be using the first model to get an idea if scab may be important in Ohio wheat this year. We are currently working with data for the southern parts of the state, Wilmington and south, which were in flower over the weekend. It appears the weather conditions, have not been highly conducive for scab development due to cooler night time temperatures and several days before flowering that no rain occurred. We will be refining our risk predictions for scab over time so visit the web site above to get current information.

B) Barley Yellow Dwarf In Wheat - Pat Lipps CORN Questions

We have had a number of reports of barley yellow dwarf in wheat, particularly in fields in southern Ohio. This virus disease is transmitted by a number of different aphids. Usually, aphids carrying the virus are blown up from more southerly regions in late summer or early fall. Early planted wheat is more likely to have problems with barley yellow dwarf because it is up when aphids are still moving about. Generally, fields planted after the Hessian fly safe date are less affected than those planted earlier.

The disease can be recognized by the distinct yellowing or reddening of the flag leaf tips. The leaf tips are discolored, but the base of the leaf generally remains green. These affected plants stand out in sharp contrast to healthy plants with normal green leaves. Also affected plants tend to be shorter than healthy plants. Color pictures and a fact sheet on this disease can be obtained on the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/byd.htm.

Wheat growers with fields affected by barely yellow dwarf need to know that there is nothing that can be done about the problem at this point. It is important to be able to tell this virus disease from fungal leaf blights, because fungicides like Tilt will do nothing to control virus diseases. Yield losses from barley yellow dwarf are usually in the 10-20% range, but if a high percentage of the plants in the field are affected the loss could be substantially greater.

C) Corn Seed Treatments: What To Expect - Pat Lipps CORN Questions

With the wet planting season facing Ohio farmers, and the threat of losses in stand due to soil borne fungal seed rot and seedling blights, there have been some questions about corn seed treatments. Growers can rest assured that seed available from all major seed corn companies are treated with combinations of fungicides to help prevent stand loss. Essentially all the seed corn available to farmers comes pretreated in the bag. Over the past five or so years there has been a great change in seed treatments on corn. Today most seed corn is treated with combinations of fungicides that include mefenoxam (Apron XL) or metalaxyl (Allegiance) to control Pythium and fludioxonil (Maxim) or captan (Captan) to control Fusarium and other seed rot fungi. These materials when used in combination provide broad-spectrum control of most disease causing fungi. Disease organisms attack seed and seedlings during extended periods of wet soil the conditions. In most cases you can expect protection for at least two weeks, unless the soil remains saturated (flooded) for a number of days after planting and before emergence. In Ohio, the use of seed treatments and improved soil drainage by tiling are important seedling blight management tools.

D) Watch For Slugs And Bean Leaf Beetles - Ron Hammond CORN Questions

Those fields that remain to be planted late because of the heavy rains this spring that have had past slug problems should be watched very closely for problems this year. Slugs have hatched and are growing. As crops finally get planted and begin to emerge, the slugs will only be that much bigger and consuming large amounts of leaf tissue. Thus, growers should watch these later-planted fields for potential problems.

With few soybean fields having been planted, the potential for higher bean leaf beetles in early-planted fields is high. Those fields already emerged will tend to serve as trap crops and receive the majority of the insects. Thus, fields already planted should be watched closely for heavier than normal defoliation. Subsequently, if these fields do have large populations this spring, they should be watched more closely throughout the summer for later population buildup during July and August.

E) Field Guide Revised - Brice Eisley CORN Questions

Need help in identifying pests in your corn, soybean, wheat and alfalfa fields? Then consider purchasing a copy of the newly revised OSU Extension Corn, Soybean, Wheat and Alfalfa Field Guide, Bulletin 827. The guide has information about the common pests (diseases, insects & weeds) that are found on these crops including colored pictures of most of the pests. The guide also contains information on fertility, herbicide, insecticide and fungicide use on these crops.

Single copies of the guide can be purchased from OSU Extension County Offices and bulk copies of the guide can be purchased by contacting:

OSU Extension Communication & Technology
Phone: 614-292-1607

F) Insect Pest Bulletin Revised - Bruce Eisley & Ron Hammond CORN Questions

Bulletin 545, Insect Pests of Field Crops, has recently been revised and is available for purchase from OSU Extension County Offices. The bulletin contains up to date information on insecticides labeled on the common insects on corn, soybean, wheat and alfalfa. The common insects are listed for each crop along with the insecticides that are labeled on these crops including rates and restrictions.

G) Alfalfa Weevil Update - Bruce Eisley & Ron Hammond CORN Questions

Populations of alfalfa weevil in untreated plots at the Western Branch declined from 3.3 larvae per stem last week to 0.6 larva per stem this week. Dead larva were found on some stems (probably killed by disease) and pupa of parasitic wasps were also found on the plants. The combination of disease and parasites apparently caused the larval population to crash. However, the larvae did considerable damage to the plants before the population crashed. The plants were severely defoliated and the plots looked gray because of the defoliation. Fields that appear to need treatment for alfalfa weevil may need to be checked again before treatment to make sure the larva have not been killed by disease or parasites.

As alfalfa harvest begins, alfalfa fields that had large numbers of alfalfa weevil larvae and were cut instead of being treated, should have the re-growth checked for alfalfa weevil feeding. In cases where re-growth appears to be retarded 7 to 10 days after harvest due to feeding activity of weevil adults or larvae, application of a stubble spray may be warranted. Although a harvest of alfalfa will generally decimate the weevil population, surviving larvae will continue feeding on re-growth and slow the second cutting. For more information, visit the Fact Sheet on Alfalfa Weevil on the Web at: http://ohioline.osu.edu/ent-fact/0032.html.

H) Wet Weather Brings Wild And Wooly Burndown Situations - Mark Loux and Jeff Stachler CORN Questions

We covered some concerns and suggestions for no-till burndown treatments in last week's newsletter. The suggestions on burndown treatments from last week apply to this week as well, but an article consisting of the word "ditto" seemed too brief, especially since continued wet weather will allow most readers plenty of time to read this week's newsletter. So, even if it's déjà vu all over again, some suggestions (updated) on burndown treatments and other concerns follow:

• We strongly suggest using a burndown treatment that provides the most complete control possible, since this helps the implementation and effectiveness of postemergence herbicides immensely!
  
• When crops are planted in late May or June, the burndown treatment controls not only all of the weeds emerging in the previous fall or early spring, but also many summer annual weeds (ragweeds, foxtails, lambsquarters, etc) that would normally have to be controlled by preemergence or postemergence herbicides. Burndown treatments in late May or June thus account for a more significant part of this year's weed control program, compared to applications in late April or early May. Take this into consideration when making a decision on burndown herbicide rates, since this may allow you to justify greater expense in a burndown treatment.
  
• Be sure to adjust glyphosate and Gramoxone rates for weed species and size. Weed size in many fields may require glyphosate rates in excess of the often "standard" rates of 26 oz (Roundup UltraMax) or 32 oz (other glyphosate products). If time allows, include 2,4-D ester to improve control of large weeds. When applying glyphosate to large weeds, avoid using fertilizer solution as the spray carrier. Weeds greater than 6 to 10 inches tall may not be controlled with Gramoxone, depending upon the species.
  
• Tillage may not adequately control large weeds, especially when soil conditions are less than ideal for tillage. Large weeds that recover after tillage and crop planting can be difficult to control with postemergence herbicides. Consider application of glyphosate or Gramoxone prior to tillage in fields where weeds are extremely large. Allow 24 to 48 hours between herbicide application and tillage for best results.
  
• By the time many fields can be planted, a number of winter annual weeds will have completed their life cycle. Once chickweed, deadnettle, and other winter annuals have gone to seed and died, it is a waste of money to try to control them. The seed they produce may result in increased winter annual populations this fall, so consider an herbicide application in November to keep them under control next spring.
  
• As we mentioned last week, delayed planting has allowed Canada thistle to develop to the point that preplant applications of glyphosate will control roots as well as shoots, and reduce the population. For most effective thistle control, use a rate of at least 26 oz (Roundup UltraMax) or 32 oz (other glyphosate products), use water as the spray carrier, and do not tank-mix with other herbicides.
  
• In corn, the addition of Balance or Hornet to standard atrazine premix products can improve control of dandelion and other emerged weeds. Atrazine works well in combination with Gramoxone, especially when the mix includes 2,4-D ester. Be aware that when applied just prior to or at the time of corn planting, 2,4-D ester can injure corn under certain rainfall conditions, when corn is planted too shallow, or when the seed furrow fails to close.
  
• Although less weedy than most fields, those fields receiving herbicide treatments last fall are becoming infested with weeds. If fields with fall treatments had been planted early, a single postemergence herbicide application may have been adequate. However, we suggest a burndown herbicide treatment in these fields to facilitate implementation of postemergence treatments. A relatively low rate of glyphosate or Gramoxone may be adequate unless Canada thistle and other perennials are present.

I) Adjusting Herbicide Programs For Late Planting - Mark Loux and Jeff Stachler CORN Questions

Consider changes to this year's herbicide program based on the delayed planting. Late planting generally reduces the need for preemergence herbicides. Reasons for this: 1) a significant percentage of this year's weeds will have been controlled by preplant tillage or burndown herbicides, and 2) the crop canopy develops more rapidly in late-planted crops. Application of persistent herbicides in late spring can increase the risk of carryover to next year's crop. Consider omitting preemergence herbicides in soybeans, and using the savings to make sure rates of burndown herbicides are adequate for those large weeds. This approach can be used in corn also, where the options in tilled fields consist of: 1) delaying application of atrazine premix products (Bicep, Harness Xtra, Guardsman Max, etc) until corn and weeds have emerged but are still less than 2 inches tall; or 2) using a total postemergence program (Accent Gold, Basis Gold, Celebrity Plus, Lightning, etc) when grass weeds are 3 to 4 inches tall. However, trying to successfully implement total postemergence programs in corn and soybeans simultaneously can be logistically difficult, and corn will typically be affected by competition with weeds earlier in the season compared to soybeans.

J) Early Postemergence Application Of Residual Corn Herbicides - Mark Loux and Jeff StachlerCORN Questions

Although very little corn has been planted, some has apparently already emerged without the benefit of a preplant or preemergence herbicide treatment. This situation may become more common in the next several weeks, as we rush to plant corn in dry periods and worry about herbicides later. All of the atrazine premix products (Guardsman, Harness Xtra, Bicep II Magnum, etc) can be applied after corn has emerged, and the atrazine should control most small emerged weeds. Some things to consider:

• Do not apply Balance, Epic, Define, Axiom, simazine, Gramoxone, or glyphosate after corn has emerged (glyphosate can be applied POST to Roundup Ready hybrids).
  
• Labels allow application up to 5- to 12-inch corn, depending upon the product. Most atrazine premix product labels specify application before weeds are in about the 2-leaf stage. Atrazine will control weeds this small, and the atrazine in premix products can be supplemented with additional atrazine (do not exceed 2 lbs atrazine total in one application). Larger weeds will often require the addition of a herbicide with foliar activity. A number of different postemergence broadleaf products can be added for large broadleaf weeds. However, an Accent-type herbicide (Accent, Basis, Option, etc) will be required for grasses larger than then the 2-leaf stage.
  
• Only Bullet, Degree Xtra, Degree, Partner, and MicroTech can be applied to emerged corn using nitrogen fertilizer solution (28%, etc) as the spray carrier. All of the other grass herbicides and atrazine premixes should be applied using water as the carrier. Corn should not be more than 6 inches tall when Degree products are applied in fertilizer solution, and air temperatures not more than 85 degrees F. Some leaf burn is likely to occur.
  
• Adding crop oil concentrate is usually necessary for effective atrazine activity on emerged weeds. As far as we know, most labels do not prohibit the use of crop oil concentrate, but consider double-checking this with a local agronomist or company representative. When tank-mixing atrazine premix products with postemergence herbicides, consult labels for spray additive recommendations to avoid corn injury.
  
• Be cautious about 2,4-D use if most of the corn has not yet emerged. Application just prior to a major rain can result in injury to corn shoots that are still underground. 2,4-D is less likely to injure corn that has already emerged.
  

K) Growing Degree Days Available For Late Corn Plantings - Peter Thomison CORN Questions

I have received several requests for information concerning growing degree days (GDDs) available for late corn plantings. The OSU Agronomy Guide 1995 edition (Table 1-1, p.4) provides GDDs for various sites in May through the 10% probability date of the first frost (first occurrence of 32 degrees F) in the fall. However, GDD accumulations based on a 10% probability of frost may be to "conservative" for use in selecting hybrids for delayed plantings, so we have provided a listing of GDDs available based on the 50% chance of frost occurrence in the fall (Table 1). Moreover this listing includes GDD accumulations through the 50% frost date for two June planting dates. The GDD accumulations shown in Table 1 were determined by H.M. Keener and R.C. Hansen and reported in OARDC Research Circular 294. The GDD values shown for the 89 Ohio locations are based on long term weather data (10-72 years).

Although there is a significant reduction in GDDs available for late planted corn compared to early planted corn, remember that GDD requirements for corn decrease by about 6.8 days for each day that planting was delayed. (See last week's C.O.R.N. article - "It Time to Switch to Earlier Maturing Corn Hybrids?" for more information on this topic.) So how do we use this information if we are trying to determine the need for switching hybrid maturities due to planting delays? Consider the following case:

Using the rate of decrease of 6.8 GDDs per day of delayed planting, a hybrid requiring 2700 GDD planted on May 1 would probably require slightly less than 2500 GDDs when planted 30 days later on May 30 [2700 GDDs - (30 days x 6.8 fewer GDDs per day of delayed planting)]. Table 1 indicates many areas in Ohio that would accumulate 2500 before an average frost date (given a May 30 planting). Because of the decrease in GDD requirements for late planted corn, most hybrid maturities commonly grown in Ohio will mature safely before frost even when planted in late May or early June.

Table 1. Average growing degree day (GDD) accumulations for 4 planting dates from May 20 to June 19 for 89 Ohio locations (source: Keener and Hanson, 1992).

Although there is a significant reduction in GDDs available for late planted corn compared to early planted corn, remember that GDD requirements for corn decrease by about 6.8 days for each day that planting was delayed. (See last week's C.O.R.N. article - "It Time to Switch to Earlier Maturing Corn Hybrids?" for more information on this topic.) So how do we use this information if we are trying to determine the need for switching hybrid maturities due to planting delays? Consider the following case:

Using the rate of decrease of 6.8 GDDs per day of delayed planting, a hybrid requiring 2700 GDD planted on May 1 would probably require slightly less than 2500 GDDs when planted 30 days later on May 30 [2700 GDDs - (30 days x 6.8 fewer GDDs per day of delayed planting)]. Because of the decrease in GDD requirements for late planted corn, most hybrid maturities commonly grown in Ohio will mature safely before frost even when planted in late May or early June.

L) Management Considerations For Late Planted Soybeans - Jim Beuerlein CORN Questions

As soybean planting date is delayed it is not necessary to change variety maturity, but seeding rates may be increased slightly. Table 2 indicates appropriate seeding rates for varying maturities, planting dates and row spacings. Seed should be planted as shallow as possible between 0.75 and 1.5 inches deep but always into moist soil. If the soil is very dry, plant at a depth of 1.0 inch in the hope that the next rain will wet the soil and seed enough for rapid germination and emergence to occur.

Regardless of planting date, we must have a healthy crop to produce maximum yield. Be sure to use fungicide treated seed to produce a healthy root system that will enable maximum growth and nutrient uptake. In a 2001 study, soybean profit was increased by $6.50 to $15.50 when seed treatments were used. Also, inoculating the seed will add 2 to 4 bushels of yield per acre at a cost of only $2 to $3 per acre. Both fungicide seed treatment and inoculation are very profitable management practices regardless of planting date.

Table 2. Suggested Seeding Rates for Combinations of Planting Date, Variety Maturity and Row Spacing.

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Steve Prochaska        Web Editor: Tom Rosati

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